Mechanisms of cadmium-stress avoidance by selenium in tomato plants

Physiological regulation underlying the alleviation of cadmium stress in maize seedlings by exogenous glycerol

Cadmium (Cd) contamination in maize poses a significant threat to global food security due to its persistent accumulation in crops. In this study, the effects of foliar application of glycerol on Cd accumulation in maize seedlings were studied. Our results demonstrated that under Cd treatment, biomass, total chlorophyll content, net photosynthetic rate (Pn), Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity, Phosphoenolpyruvate carboxylase (PEPC) activity, sucrose levels, and carbohydrate levels in maize seedlings significantly increased after glycerol application. H2O2 and MDA levels in both the aboveground and belowground portions of the maize plants significantly decreased. Moreover, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities in the aboveground parts significantly increased. Notably, maize plants used glycerol to chelate Cd, which was fixed within the cell wall and soluble fraction of the roots, reducing Cd transport to the shoots and significantly lowering the Cd transport coefficient (TF). Transcriptomic data suggested that glycerol-mediated alleviation of Cd stress in maize seedlings may be associated with phenylpropanoid biosynthesis, plant-pathogen interactions and photosynthesis pathways. These molecular patterns align with the observed physiological improvements. This study provided a novel approach to effectively alleviate excessive Cd in maize and suggested possible applications of glycerol in cultivating plant resistance to heavy metals.

Selenium Improves Yield and Quality in Prunella vulgaris by Regulating Antioxidant Defense, Photosynthesis, Growth, Secondary Metabolites, and Gene Expression Under Acid Stress

Prunella vulgaris, an essential component of traditional Chinese medicine, is suitable for growing in soil with a pH value ranging from 6.5 to 7.5. However, it is primarily cultivated in acidic soil regions of China, where its growth is frequently compromised by acidic stress. Selenium (Se) has been recognized for its potential to enhance stress tolerance in plants. However, its role in acid-stress-induced oxidative stress is not clear. In this study, the effects of varying Se concentrations on the growth and quality of P. vulgaris under acidic stress were investigated. The results showed that acid stress enhanced antioxidant enzyme activities, non-enzymatic antioxidant substances, and osmolyte content, accompanied by an increase in oxidant production and membrane damage. Furthermore, it decreased the photosynthetic capacity, inhibited root and shoot growth, and diminished the yield of P. vulgaris. In contrast, exogenous application of Se, particularly at 5 mg L-1, markedly ameliorated these adverse effects. Compared to acid-stressed plants, 5 mg L-1 Se treatment enhanced superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione peroxidase activities by 150.19%, 54.94%, 43.43%, and 45.55%, respectively. Additionally, soluble protein, soluble sugar, and proline contents increased by 11.75%, 23.32%, and 40.39%, respectively. Se application also improved root architecture and alleviated membrane damage by reducing hydrogen peroxide, superoxide anion, malondialdehyde, and electrolyte leakage levels. Furthermore, it significantly enhanced the photosynthetic capacity by elevating pigment levels, the performance of PSI and PSII, electron transfer, and the coordination of PSI and PSII. Consequently, plant growth and spica weight were significantly promoted, with a 12.50% increase in yield. Moreover, Se application upregulated key genes involved in flavonoid and phenolic acid metabolic pathways, leading to elevated levels of total flavonoids, caffeic acid, ferulic acid, rosmarinic acid, and hyperoside by 31.03%, 22.37%, 40.78%, 15.11%, and 20.84%, respectively, compared to acid-stressed plants. In conclusion, exogenous Se effectively alleviated the adverse effects of acid stress by improving the antioxidant system, growth, and photosynthetic capacity under acid stress, thus enhancing the yield and quality of P. vulgaris.

Exogenous selenium enhances cadmium stress tolerance by improving physiological characteristics of Artemisia argyi seedlings

The contamination of Chinese medicinal materials with cadmium (Cd) is a pressing global issue that poses significant risks to human health. The beneficial effects of selenium (Se) have been established in improving plant growth and reducing Cd accumulation in plant under Cd stress. This study employed soil cultivation experiments to investigate the remediation effects of exogenous Se (0, 0.5, 1, and 2 mg kg⁻1) under varying levels of Cd stress (0, 0.6 and 4 mg kg⁻1). The findings revealed that Cd stress markedly impaired seedling growth, biomass, and physiological characteristics in Artemisia argyi. Regardless of Cd levels, exogenous Se significantly enhanced seedling biomass, improved antioxidant enzyme activity, and increased the plant's antioxidant capacity, thereby mitigating Cd stress. Additionally, exogenous Se promoted A. argyi plant growth, decreased malondialdehyde (MDA) content in the shoots, and under two Cd stress environments of 0.6 and 4 mg kg⁻1, the application of 1 mg kg⁻1 Se reduced the Cd content in the aboveground parts of seedlings by 31.99 and 82.21%, respectively. We conclude 1 mg kg⁻1 Se could represent a promising strategy to contribute to the development and sustainability of crop production on soils contaminated with Cd at a concentration of up to 0.6 and 4 mg kg⁻1. These results indicate that exogenous Se activates physiological and biochemical defense mechanisms in A. argyi seedlings against Cd stress, offering a foundation for cultivating high-yield, high-quality A. argyi in Cd-contaminated soils.

Synergistic mitigation of cadmium stress in rice (Oryza sativa L.) through combined selenium, calcium, and magnesium supplementation

Rice is susceptible to cadmium (Cd) accumulation, which poses a threat to human health. Traditional methods for mitigating moderately contaminated soils can be impractical or prohibitively expensive, necessitating innovative approaches to reduce Cd uptake in rice. Nutrient management has emerged as a promising solution by leveraging the antagonistic interactions between nutrients and cadmium. However, the research on the synergistic effects of multiple nutrients on Cd toxicity in rice is limited. To address this limitation, pot experiments was utilized to investigate the combined effects of selenium (Se), calcium (Ca), and magnesium (Mg) denoted as (SeCM) on Cd uptake and translocation in rice. The synergistic application of SeCM reduced grain Cd levels by 55.0%, surpassing the individual effects of Se (42.1%) and CM (40.5%), and bringing Cd content below the safe consumption limits. SeCM treatment exhibited multiple beneficial effects: it decreased malondialdehyde (MDA) levels, enhanced catalase (CAT), peroxidase (POD) and glutathione (GSH) enzyme activities, limited Cd translocation from roots to shoots, promoted iron plaque formation, and reduced Cd transfer from soil to iron plaque and subsequently to rice grains. Correlation analysis revealed strong negative relationships between rice Cd content, Cd translocation factors, and the translocation factors of selenium, calcium, and magnesium. These findings suggest that selenium, calcium, and magnesium collaboratively mitigate Cd toxicity through antagonistic and competitive interactions. These nutrients enhance the uptake of beneficial elements, while competitively inhibiting the translocation and accumulation of Cd in rice plants. SeCM application offers a promising strategy for producing nutrient-rich, and Cd-safe rice in contaminated soils.

Selenite improves growth by modulating phytohormone pathways and reprogramming primary and secondary metabolism in tomato plants

Selenium (Se) is an essential micronutrient in organisms that has a significant impact on physiological activity and gene expression in plants, thereby affecting growth and development. Humans and animals acquire Se from plants. Tomato (Solanum lycopersicum L.) is an important vegetable crop worldwide. Improving the Se nutrient level not only is beneficial for growth, development and stress resistance in tomato plants but also contributes to improving human health. However, the molecular basis of Se-mediated tomato plant growth has not been fully elucidated. In this study, using physiological and transcriptomic analyses, we investigated the effects of a low dosage of selenite [Se(Ⅳ)] on tomato seedling growth. Se(IV) enhanced the photosynthetic efficiency and increased the accumulation of soluble sugars, dry matter and organic matter, thereby promoting tomato plant growth. Transcriptome analysis revealed that Se(IV) reprogrammed primary and secondary metabolic pathways, thus modulating plant growth. Se(IV) also increased the concentrations of auxin, jasmonic acid and salicylic acid in leaves and the concentration of cytokinin in roots, thus altering phytohormone signaling pathways and affecting plant growth and stress resistance in tomato plants. Furthermore, exogenous Se(IV) alters the expression of genes involved in flavonoid biosynthesis, thereby modulating plant growth and development in tomato plants. Taken together, these findings provide important insights into the regulatory mechanisms of low-dose Se(IV) on tomato growth and contribute to the breeding of Se-accumulating tomato cultivars.

Cadmium uptake and detoxification in tomato plants: Revealing promising targets for genetic improvement

Cadmium (Cd) is a hazardous heavy metal known for its detrimental effects on plants, human health, and the environment. This review article delves into the dynamics of Cd uptake, long-distance transport, and its impact on plant performance, with a specific focus on tomato plants. The process of Cd uptake by roots and its subsequent long-distance transport in the xylem and phloem are explored to understand how Cd influences plants operation. The toxic effects of Cd on tomato plants are discussed, highlighting on the challenges it poses to plant growth and development. Furthermore, the review investigates various Cd tolerance mechanisms in plants, including avoidance or exclusion by the root cell wall, root-to-shoot translocation, detoxification pathways, and antioxidative defence systems against Cd-induced stress. In addition, the transcriptomic analyses of tomato plants under Cd stress provide insights into the molecular responses and adaptations of plants to Cd toxicity. Overall, this comprehensive review enhances our understanding of Cd-plant interactions and reveal promising genes for tomato genetic improvement to increase its tolerance to cadmium.

Dynamic interplay of reactive oxygen and nitrogen species (ROS and RNS) in plant resilience: unveiling the signaling pathways and metabolic responses to biotic and abiotic stresses

KEY MESSAGE

Plants respond to environmental challenges by producing reactive species such as ROS and RNS, which play critical roles in signaling pathways that lead to adaptation and survival strategies. Understanding these pathways, as well as their detection methods and effects on plant development and metabolism, provides insight into increasing crop tolerance to combined stresses. Plants encounter various environmental stresses (abiotic and biotic) that affect plant growth and development. Plants sense biotic and abiotic stresses by producing different molecules, including reactive species, that act as signaling molecules and stimulate secondary messengers and subsequent gene transcription. Reactive oxygen and nitrogen species (ROS and RNS) are produced in both physiological and pathological conditions in the plasma membranes, chloroplasts, mitochondria, and endoplasmic reticulum. Various techniques, including spectroscopy, chromatography, and fluorescence methods, are used to detect highly reactive, short-half-life ROS and RNS either directly or indirectly. In this review, we highlight the roles of ROS and RNS in seed germination, root development, senescence, mineral nutrition, and post-harvest control. In addition, we provide information on the specialized metabolism involved in plant growth and development. Secondary metabolites, including alkaloids, flavonoids, and terpenoids, are produced in low concentrations in plants for signaling and metabolism. Strategies for improving crop performance under combined drought and pathogen stress conditions are discussed in this review.

Enhancement of Nutritional Substance, Trace Elements, and Pigments in Waxy Maize Grains through Foliar Application of Selenite

Selenium (Se) is a micronutrient known for its essential role in human health and plant metabolism. Waxy maize (Zea mays L. sinensis kulesh)-known for its high nutritional quality and distinctive flavor-holds significant consumer appeal. Therefore, this study aims to assess the effects of foliar Se spraying on the nutritional quality of waxy maize grains, with a focus on identifying varietal differences and determining optimal Se dosage levels for maximizing nutritional benefits. We employed a two-factor split-plot design to assess the nutritional quality, trace elements, and pigment content of jinnuo20 (J20) and caitiannuo1965 (C1965) at the milk stage after being subjected to varying Se doses sprayed on five leaves. Our findings indicate superior nutrient content in J20 compared to C1965, with both varieties exhibiting optimal quality under Se3 treatment, falling within the safe range of Se-enriched agricultural products. JS3 (0.793) demonstrated the highest overall quality, followed by JS2 (0.606), JS4 (0.411), and JS1 (0.265), while CS0 had the lowest (-0.894). These results underscore the potential of foliar biofortification to enhance the functional component contents of waxy maize grains.

Differential responses of chili varieties grown under cadmium stress

Heavy metal cadmium (Cd) naturally occurs in soil and is a hazardous trace contaminant for humans, animals, and plants. The main sources of Cd pollution in soil include overuse of phosphatic fertilizers, manure, sewage sludge, and aerial deposition. That's why an experiment was conducted to analyze the effect of Cd toxicity in Capsicum annuum L. by selecting its seven varieties: Hybrid, Desi, Sathra, G-916, BR-763, BG-912, and F1-9226. Cadmium was spiked in soil with four levels, i.e., (0, 3, 4, and 5 mg Cd kg- 1 of soil) for a week for homogeneous dispersion of heavy metal. Chili seeds were sown in compost-filled loamy soil, and 25-day-old seedlings were transplanted into Cd-spiked soil. Cadmium increasing concentration in soil decreased chili growth characteristics, total soluble sugars, total proteins, and amino acids. On the other hand, the activities of antioxidant enzymes were increased with the increasing concentration of Cd in almost all the varieties. Treatment 5 mg Cd/kg application caused - 197.39%, -138.78%, -60.77%, -17.84%, -16.34%, -11.82% and - 10.37% decrease of carotenoids level in chili V2 (Desi) followed by V4 (G-916), V1 (Hy7brid), V7 (F1-9226), V6 (BG-912), V5 (BR-763) and V3 (Sathra) as compared to their controls. The maximum flavonoids among varieties were in V5 (BR-763), followed by V6 (BG-912), V7 (F1-9226), V3 (Sathra) and V1 (Hybrid). Flavonoids content was decreased with - 37.63% (Sathra), -34.78% (Hybrid), -33.85% (G-916), -31.96% (F1-9226), -31.44% (Desi), -30.58% (BR-763), -22.88% (BG-912) as compared to their control at 5 mg Cd/kg soil stress. The maximum decrease in POD, SOD, and CAT was - 31.81%, -25.98%, -16.39% in chili variety V7 (F1-9226) at 5 mg Cd/kg stress compared to its control. At the same time, maximum APX content decrease was - 82.91%, followed by -80.16%, -65.19%, -40.31%, -30.14%, -10.34% and - 6.45% in V4 (G-916), V2 (Desi), V3 (Sathra), V6 (BG-912), V1 (Hybrid), V7 (F1-9226) and V5 (BR-763) at 5 mg Cd/kg treatment as compared to control chili plants. The highest CAT was found in 5 chili varieties except Desi and G-916. Desi and G-916 varieties. V5 (BR-763) and V6 (BG-912) were susceptible, while V1 (Hybrid), V3 (Sathra), and V7 (F1-9226) were with intermediate growth attributes against Cd stress. Our results suggest that Desi and G-916 chili varieties are Cd tolerant and can be grown on a large scale to mitigate Cd stress naturally.

Review on Pesticide Abiotic Stress over Crop Health and Intervention by Various Biostimulants

Plants are essential for life on earth, and agricultural crops are a primary food source for humans. For the One Health future, crop health is crucial for safe, high-quality agricultural products and the development of future green commodities. However, the overuse of pesticides in modern agriculture raises concerns about their adverse effects on crop resistance and product quality. Recently, biostimulants, including microecological bacteria agents and nanoparticles, have garnered worldwide interest for their ability to sustain plant health and enhance crop resistance. This review analyzed the effects and mechanisms of pesticide stress on crop health. It also investigated the regulation of biostimulants on crop health and the multiomics mechanism, combining research on nanoselenium activating various crop health aspects conducted by the authors' research group. The paper helps readers understand the impact of pesticides on crop health and the positive influence of various biostimulants, especially nanomaterials and small molecules, on crop health.

Investigation of the role of TmMYB16/123 and their targets (TmMTP1/11) in the tolerance of Taxus media to cadmium

The toxicity and stress caused by heavy metal contamination has become an important constraint to the growth and flourishing of trees. In particular, species belonging to the genus Taxus, which are the only natural source for the anti-tumor medicine paclitaxel, are known to be highly sensitive to environmental changes. To investigate the response of Taxus spp. to heavy metal stress, we analyzed the transcriptomic profiles of Taxus media trees exposed to cadmium (Cd2+). In total, six putative genes from the metal tolerance protein (MTP) family were identified in T. media, including two Cd2+ stress inducible TMP genes (TmMTP1, TmMTP11 and Taxus media). Secondary structure analyses predicted that TmMTP1 and TmMTP11, which are members of the Zn-CDF and Mn-CDF subfamily proteins, respectively, contained six and four classic transmembrane domains, respectively. The introduction of TmMTP1/11 into the ∆ycf1 yeast cadmium-sensitive mutant strain showed that TmMTP1/11 might regulate the accumulation of Cd2+ to yeast cells. To screen the upstream regulators, partial promoter sequences of the TmMTP1/11 genes were isolated using the chromosome walking method. Several myeloblastosis (MYB) recognition elements were identified in the promoters of these genes. Furthermore, two Cd2+-induced R2R3-MYB TFs, TmMYB16 and TmMYB123, were identified. Both in vitro and in vivo assays confirmed that TmMTB16/123 play a role in Cd2+ tolerance by activating and repressing the expression of TmMTP1/11 genes. The present study elucidated new regulatory mechanisms underlying the response to Cd stress and can contribute to the breeding of Taxus species with high environmental adaptability.

Aphanothece sp. as promising biostimulant to alleviate heavy metals stress in Solanum lycopersicum L. by enhancing physiological, biochemical, and metabolic responses

Heavy metals (H.M) are a major environmental concern around the world. They have harmful impact on plant productivity and pose a serious risk to humans and animals health. In the present study, we investigated the effect of Aphanothece crude extract (ACE) on physiological, biochemical, and metabolic responses of tomato plant exposed to 2 mM Pb and Cd. The results showed a significant reduction of tomato plant weights and perturbation in nutrients absorption under 2 mM Pb and Cd conditions. Moreover, ACE treatment showed a significant enhancement of plant biomass compared to plants under Pb and Cd. On the other hand, ACE application favoured H.M accumulation in root and inhibited their translocation to shoot. In addition, ACE treatment significantly enhanced several stress responses in plant under Pb and Cd stress such as scavenging enzymes and molecules: POD, CAT, SOD, proline, and polyphenols etc. Furthermore, ACE treatment showed remodulation of metabolic pathways related to plant tolerance such as wax construction mechanism, particularly SFA, UFA, VLFA, alkanes, alkenes, and sterols biosynthesis to enhance tolerance and resistance to H.M stress. In the present study, we emphasized that ACE alleviates H.M stress by minimizing metal translocation to above-part of plant and enhancing plant growth, nutrients absorption, and biochemical responses.

Sly-miR398 Participates in Cadmium Stress Acclimation by Regulating Antioxidant System and Cadmium Transport in Tomato (Solanum lycopersicum)

Cadmium (Cd) pollution is one of the major threats in agricultural production, and can cause oxidative damage and growth limitation in plants. MicroRNA398 (miR398) is involved in plant resistance to different stresses, and the post-transcriptional regulation of miR398 on CSDs plays a key role. Here, we report that miR398 was down-regulated in tomato in response to Cd stress. Simultaneously, CSD1 and SOD were up-regulated, with CSD2 unchanged, suggesting CSD1 is involved in miR398-induced regulation under Cd stress. In addition, the role of miR398 in Cd tolerance in tomato was evaluated using a transgenic line overexpressing MIR398 (miR398#OE) in which the down-expression of miR398 was disrupted. The results showed that Cd stress induced more significant growth inhibition, oxidative damage, and antioxidant enzymes disorder in miR398#OE than that in wild type (WT). Moreover, higher Cd concentration in the shoot and xylem sap, and net Cd influx rate, were observed in miR398#OE, which could be due to the increased Cd uptake genes (IRT1, IRT2, and NRAMP2) and decreased Cd compartmentalization gene HMA3. Overall, our results indicate that down-regulated miR398 plays a protective role in tomato against Cd stress by modulating the activity of antioxidant enzymes and Cd uptake and translocation.

Interaction between selenium and essential micronutrient elements in plants: A systematic review

Nutrient imbalance (i.e., deficiency and toxicity) of microelements is an outstanding environmental issue that influences each aspect of ecosystems. Although the crucial roles of microelements in entire lifecycle of plants have been widely acknowledged, the effective control of microelements is still neglected due to the narrow safe margins. Selenium (Se) is an essential element for humans and animals. Although it is not believed to be indispensable for plants, many literatures have reported the significance of Se in terms of the uptake, accumulation, and detoxification of essential microelements in plants. However, most papers only concerned on the antagonistic effect of Se on metal elements in plants and ignored the underlying mechanisms. There is still a lack of systematic review articles to summarize the comprehensive knowledge on the connections between Se and microelements in plants. In this review, we conclude the bidirectional effects of Se on micronutrients in plants, including iron, zinc, copper, manganese, nickel, molybdenum, sodium, chlorine, and boron. The regulatory mechanisms of Se on these micronutrients are also analyzed. Moreover, we further emphasize the role of Se in alleviating element toxicity and adjusting the concentration of micronutrients in plants by altering the soil conditions (e.g., adsorption, pH, and organic matter), promoting microbial activity, participating in vital physiological and metabolic processes, generating element competition, stimulating metal chelation, organelle compartmentalization, and sequestration, improving the antioxidant defense system, and controlling related genes involved in transportation and tolerance. Based on the current understanding of the interaction between Se and these essential elements, future directions for research are suggested.

Advances in physiological mechanisms of selenium to improve heavy metal stress tolerance in plants

Selenium (Se) is a metalloid mineral nutrient for human and animal health. Plants are the main foodstuff source of the Se intake of humans. For plants, the addition of an appropriate amount of Se could promotes growth and development, and improves the tolerance to environmental stress, especially stress from some of heavy metals (HM) stress, such as cadmium (Cd) and mercury (Hg). This paper mainly reviews and summarizes the physiological mechanism of Se in enhancing HM stress tolerance in plants. The antagonistic effect of Se on HM is a comprehensive effect that includes many physiological mechanisms. Se can promote the removal of excessive reactive oxygen species and reduce the oxidative damage of plant cells under HM elements stress. Se participates in the regulation of the transportation and distribution of HM ions in plants, and alleviates the damage caused by of HM stress. Moreover, Se combine with HM elements to form Se-HM complexes and promote the production of phytochelatins (PCs), thereby reducing the accumulation of HM ions in plants. Overall, Se plays an important role in plant response to HM stress, but current studies mainly focus on physiological mechanism, and further in-depth study on the molecular mechanism is essential to confirm the participation of Se in plant response to environmental stress. This review helps to comprehensively understand the physiological mechanism of Se in plant tolerance against to HM stress of plants, and provides important theoretical support for the practical application of Se in environmental remediation and agricultural development.

Selenium improved the combined remediation efficiency of Pseudomonas aeruginosa and ryegrass on cadmium-nonylphenol co-contaminated soil

Most chemical plant wastewater contains both organic and inorganic pollutants, which are easy to diffuse along with surface runoff. The combined pollution of nonylphenol (NP) and cadmium (Cd) in soil is a serious problem that has not attracted enough attention. Based on the effects of selenium (Se) and Pseudomonas aeruginosa (P. aeruginosa) on plant and soil microbial communities, we speculated that the application of Se and P. aeruginosa in soil could improve the phytoremediation efficiency of ryegrass on contaminated soil. In this study, pot experiments with Cd and NP co-contaminated soil were conducted, and the results showed that application of P. aeruinosa alone could improve the removal rates of NP and Cd by ryegrass, and the supplementary of Se further enhanced the effect of micro-phyto remediation, with the highest removal rates of NP and Cd were 79.6% and 49.4%, respectively. The application of P. aeruginosa plus Se reduced the adsorption of Cd and NP through C-O and Si-O-Fe of the soil, changed the enzyme activity, and also affected the changing trend of the microbial community in soil. Pseudomonas, Sphingomonadales, Nitrospira, and other beneficial bacteria were enriched after a 60-day period with P. aeruginosa and Se treatment, thus promoting the removal of NP and Cd. In light of the above results, we suggest that P. aeruginosa application can efficiently facilitate the phytoremediation of ryegrass on Cd-NP co-contaminated soil, and Se supplementation in soil showed the synergistic effect on the remediation.

Sustainable management of cadmium-contaminated soils as affected by exogenous application of nutrients: A review

Cadmium (Cd) pollution in arable land is of great concern as it impairs plant growth and further threats human health via food-chain. Exogenous supplementation of nutrients is an environmentally-friendly, cost-effective, convenient and feasible strategy for regulating Cd uptake, transport and accumulation in plants. To sustain Cd-contaminated soils management, on the one hand, a low level of the Cd-contaminated soil is expected to cultivate crops with decreased Cd accumulation as affected by exogenous nutrients application, on another hand, a high level of the Cd-contaminated soil is suggested to cultivate phytoextraction plants with increased Cd accumulation as affected by exogenous nutrients application. Nevertheless, effects of nutrients on Cd accumulation in plants are still ambiguous. Thus, data of Cd accumulation in shoots of plants as affected by exogenous application of nutrients were collected from previously published articles between 2005 and 2021 in the present study. According to the data, exogenous supply of calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn) and silicon (Si) to a larger extent decrease Cd amounts in shoots of plants. By contrast, exogenous nitrogen (N), and deficient Ca, Mg and Fe supply have a great possibility to increase Cd amounts in shoots of plants. Although exogenous application of phosphorus (P), sulfur (S), potassium (K), zinc (Zn) and selenium (Se) have a great opportunity to increase biomass, they show different effects on Cd concentrations. As a result, the odds are even for increasing and decreasing Cd amounts in shoots of plants. Taken together, exogenous application of Ca, Mg, Fe, Mn and Si might decrease Cd accumulation in plants that are recommended for crops production. Exogenous N and deficient Ca, Mg and Fe supply might increase Cd accumulation in plants that are recommended for phytoextraction plants. Exogenous application of P, S, K, Zn and Se have half a chance to increase or decrease Cd accumulation in plants. Therefore, dosages, forms and species should be taken into account when exogenous P, S, K, Zn and Se are added.

The Effect of Foliar Selenium (Se) Treatment on Growth, Photosynthesis, and Oxidative-Nitrosative Signalling of Stevia rebaudiana Leaves

Selenium (Se) enrichment of Stevia rebaudiana Bertoni can serve a dual purpose, on the one hand to increase plant biomass and stress tolerance and on the other hand to produce Se fortified plant-based food. Foliar Se spraying (0, 6, 8, 10 mg/L selenate, 14 days) of Stevia plantlets resulted in slightly decreased stevioside and rebaudioside A concentrations, and it also caused significant increment in stem elongation, leaf number, and Se content, suggesting that foliar Se supplementation can be used as a biofortifying approach. Furthermore, Se slightly limited photosynthetic CO2 assimilation (AN, gsw, Ci/Ca), but exerted no significant effect on chlorophyll, carotenoid contents and on parameters associated with photosystem II (PSII) activity (FV/FM, F0, Y(NO)), indicating that Se causes no photodamage in PSII. Further results indicate that Se is able to activate PSI-cyclic electron flow independent protection mechanisms of the photosynthetic apparatus of Stevia plants. The applied Se activated superoxide dismutase (SOD) isoenzymes (MnSOD1, FeSOD1, FeSOD2, Cu/ZnSOD1, Cu/ZnSOD2) and down-regulated NADPH oxidase suggesting the Se-induced limitation of superoxide anion levels and consequent oxidative signalling in Stevia leaves. Additionally, the decrease in S-nitrosoglutathione reductase protein abundance and the intensification of protein tyrosine nitration indicate Se-triggered nitrosative signalling. Collectively, these results suggest that Se supplementation alters Stevia shoot morphology without significantly affecting biomass yield and photosynthesis, but increasing Se content and performing antioxidant effects, which indicates that foliar application of Se may be a promising method in Stevia cultivation.

Melatonin Participates in Selenium-Enhanced Cold Tolerance of Cucumber Seedlings

Melatonin is an important and widespread plant hormone. However, the underlying physiological and molecular mechanisms of melatonin as a secondary messenger in improving cold tolerance by selenium are limited. This study investigated the effects of selenite on the cold stress of cucumber seedlings. The results showed that exogenous application of selenite improved the cold tolerance of cucumber seedlings, which was dependent on the concentration effect. In the present experiment, 1 μM of selenite showed the best effect on alleviating cold stress. Interestingly, we found that in the process of alleviating cold stress, selenite increased the content of endogenous melatonin by regulating the expression of melatonin biosynthesis genes (TDC, T5H, SNAT, and COMT). To determine the interrelation between selenite and melatonin in alleviating cold stress, melatonin synthesis inhibitor p-chlorophenylalanine and melatonin were used for in-depth study. This study provides a theoretical basis for cucumber cultivation and breeding.

Coffea arabica seedlings genotypes are tolerant to high induced selenium stress: Evidence from physiological plant responses and antioxidative performance

Selenium (Se) is considered a beneficial element to higher plants based on its regulation of antioxidative system under abiotic or biotic stresses. However, the limit of beneficial and toxic physiological effects of Se is very narrow. In the present study, the antioxidant performance, nutritional composition, long-distance transport of Se, photosynthetic pigments, and growth of Coffea arabica genotypes in response to Se concentration in solution were evaluated. Five Coffea arabica genotypes (Obatã, IPR99, IAC125, IPR100 and Catucaí) were used, which were grown in the absence and presence of Se (0 and 1.0 mmol L^-1) in nutrient solution. The application of 1 mmol L^-1 Se promoted root browning in all genotypes. There were no visual symptoms of leaf toxicity, but there was a reduction in the concentration of phosphorus and sulfur in the shoots of plants exposed to high Se concentration. Except for genotype Obatã, the coffee seedlings presented strategies for regulating Se uptake by reducing long-distance transport of Se from roots to shoots. The concentrations of total chlorophyll, total pheophytin, and carotenoids were negatively affected in genotypes Obatã, IPR99, and IAC125 upon exposure to Se at 1 mmol L^-1. H₂O₂ production was reduced in genotypes IPR99, IPR100, and IAC125 upon exposure to Se, resulting in lower activity of superoxide dismutase (SOD), and catalase (CAT). These results suggest that antioxidant metabolism was effective in regulating oxidative stress in plants treated with Se. The increase in sucrose, and decrease in SOD, CAT and ascorbate peroxidase (APX) activities, as well as Se compartmentalization in the roots, were the main biochemical and physiological modulatory effects of coffee seedlings under stress conditions due to excess of Se.